1. Field of the Invention
The present invention relates to a pneumatic tire, and in more detail, the present invention relates to the pneumatic tire that inhibits the generation of so-called stone-biting, a phenomenon in which stones are caught in the tire grooves and cannot be removed, while securing the traction performance and the drainage performance.
2. Description of the Prior Art
In order to obtain desired performances including drainage performance, traction performance, braking performance, and the like, main grooves extending in the tire circumferential direction and transverse grooves extending in the tire width direction are formed on a tread. When stones are caught in the grooves and cannot be removed therefrom, sometimes the stones proceed in the direction of groove bottoms, thereby damaging the groove bottoms. When the stones proceed further into the grooves, belt layers and auxiliary belt layers are damaged, enhancing the risk of causing failure. In particular, main grooves are likely to be damaged since deformation of the grooves by tire rotation is little. In order to prevent such catching of stones, the pneumatic tire provided with protrusions (called stone ejectors) at the center in the bottom of the main grooves so that the stones do not proceed into the grooves is known (Patent document 1: Unexamined Japanese Laid-Open Patent Publication No. 2002-293110).
However, when the protrusions with heights capable of satisfactorily preventing the generation of the catching of stones are provided at the center in the bottom of the main grooves, the drainage performance of the main grooves get greatly degraded. Also, cracks are likely to occur at the joining portion between the protrusion and the groove bottom since the protrusion gets more deformable when the stones proceed into the grooves. Therefore, it has been difficult to realize both improvement in the drainage performance and prevention of the catching of stones.
Therefore, the object of the present invention is to prevent generation of the catching of stones, while maintaining the good drainage performance.